The Roof Rack

A roof rack is the most tempting and most physics-hostile place to put anything, because it works directly against the rules the module has been building. Three things, every time:

One — centre of gravity. Weight on the roof is the highest possible placement, so it has the largest effect on roll. A roof-loaded car corners and swerves differently, and is measurably more prone to rolling in an emergency manoeuvre. So: roof racks are for light, bulky items — a mattress, empty containers, bedding — never for heavy ones. Heavy goes in the boot, low, against the seat-back. If it's heavy and it won't fit inside, the honest answer is a second trip or a different vehicle.

Two — securing. Roof loads face the full 80%/50% force set plus wind, and they're the most likely of all loads to depart the vehicle entirely, becoming an obstacle for everyone behind you. Rated straps, multiple directions, checked after the first few kilometres — the settling re-check matters most here, because roof loads are precisely where tension drops.

Three — height. Height is the rule people forget until it's expensive: you no longer know how tall your vehicle is. Parking structures, low branches, overhangs and barriers become genuine hazards. Measure or estimate the loaded height and carry it in your head for the whole journey.